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Old July 28th, 2021, 05:25 AM   #1
koyeap
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AB PLC5 BTW/BTR Block

Dear Pros,

Need help on converting PLC5 to Studio 5000.
I found few BTW/BTR block pointing back to Rack 000, group 0, module 0, which should be the CPU module. The weird part is the length is 0. Is length 0 mean the BTW/BTR block not in use anymore?

Or this is actually some technique to get some hardware status?
Attached some print screen for the logic.
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File Type: png Print Screen 2.PNG (102.4 KB, 12 views)
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Old July 28th, 2021, 06:18 AM   #2
drbitboy
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Old July 28th, 2021, 08:50 AM   #3
Operaghost
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The CPU in a PLC-5 system does not have a rack address. Rack 0, Group 0 Module 0 would be the first slot to the right of the CPU. The length of 0 means whatever that module has available (read) or will accept (write). It was a default setting for when you didn't want to have to look up the actual number of words to read or write. When managing memory, it meant that you had to assume it would use 64 words. You wouldn't just say 64 (the maximum) because if the module had less than that it would cause an instruction error. So using 0 was very common.

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Old July 28th, 2021, 02:48 PM   #4
GaryS
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It looks like they wrote the block transfer and then never actually finished
Length of 0
I believe the rack 0 and group 0 I. The processor
In logix5000 you need need to use messaging
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Old July 28th, 2021, 03:42 PM   #5
Operaghost
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Quote:
Originally Posted by Operaghost View Post
The CPU in a PLC-5 system does not have a rack address. Rack 0, Group 0 Module 0 would be the first slot to the right of the CPU. The length of 0 means whatever that module has available (read) or will accept (write). It was a default setting for when you didn't want to have to look up the actual number of words to read or write. When managing memory, it meant that you had to assume it would use 64 words. You wouldn't just say 64 (the maximum) because if the module had less than that it would cause an instruction error. So using a length of 0 was very common.

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Old July 28th, 2021, 08:40 PM   #6
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oh I see, thanks a lot! sorry i missed out the 0 is reserve for maximum in manual.

Next module to CPU is a backup comm module(BCM), which mean this block transfer is for redundancy data exchange purpose? or is connect to 3rd parties devices?
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Old July 28th, 2021, 10:24 PM   #7
koyeap
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Quote:
Originally Posted by koyeap View Post
oh I see, thanks a lot! sorry i missed out the 0 is reserve for maximum in manual.

Next module to CPU is a backup comm module(BCM), which mean this block transfer is for redundancy data exchange purpose? or is connect to 3rd parties devices?
Since I am going to upgrade the PLC5 to 1756 Series, which mean if this is for redundancy purpose then i can ignore the BTW/BTR in new logic right?

Thanks
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Old July 29th, 2021, 09:21 AM   #8
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The BTR/BTW for the BCM modules was a method to transfer data from one CPU to another. All the remote I/O data was automatically transferred. It was a way to synchronize any other data between the two CPUs. But they are running identical programs so they should have the same data anyway. I never used this myself. To me it seemed unnecessary. But I'm sure someone can identify where they needed this.

This would be unnecessary in the ControlLogix. Synchronization of redundant systems is handled without the need for any logic messaging.

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Old July 30th, 2021, 03:30 AM   #9
koyeap
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Dear Operaghost,

Thanks a lot for all the valuable info!
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